Обсуждение: 'on insert' rules and defaults

Playing around with rules and views, I noticed the
following:

CREATE TABLE t ( i INTEGER,b BOOLEAN DEFAULT false
);

CREATE VIEW v ASSELECT * FROM t;

CREATE RULE v_insert ASON INSERT TO v DO INSTEADINSERT INTO t values ( NEW.i, NEW.b);

mhh=# insert into v values ( 1 );
INSERT 50199 1
mhh=# select * from v;i | b 
---+---1 | 
(1 row)

In other words, the default is not honored. Is there a way to
write the rule so that default on 'b' is honored?

I found the following to work. But the combinatorial explosion
for multiple fields is a killer.

CREATE RULE v_insert_null ASON INSERT TO v WHERE NEW.b IS NULL DO INSTEADINSERT INTO t values (NEW.i);
CREATE RULE v_insert_not_null ASON INSERT TO v WHERE NEW.b IS NOT NULL DO INSTEADINSERT INTO t values (NEW.i, NEW.b);

I also thought about COALESCE:

CREATE RULE v_insert ASON INSERT TO v DO INSTEADINSERT INTO t values (NEW.i, COALESCE(NEW.b, false));

But then two places have to know about the default value.

Any other suggestions?

-- 

Mark Hollomon
mhh@nortelnetworks.com
ESN 451-9008 (302)454-9008

"Mark Hollomon" <mhh@nortelnetworks.com> writes:
> In other words, the default is not honored.

Right, since the INSERT written in the rule provides an explicit
specification of what should be inserted into t.  NEW.b is NULL
and that's what gets inserted.

> I also thought about COALESCE:

> CREATE RULE v_insert AS
>     ON INSERT TO v DO INSTEAD
>     INSERT INTO t values (NEW.i, COALESCE(NEW.b, false));

> But then two places have to know about the default value.

Another problem with that is that there's no way to specify insertion
of a NULL into b.

> Any other suggestions?

You really want default substitution to be done by the parser.
Any later is too late because you won't be able to tell an explicit
NULL from a defaulted column.

I haven't tried it, but I think it would work to declare the "view"
as a real table and then attach the rules to it:

CREATE TABLE t ( i INTEGER,b BOOLEAN DEFAULT false
);

CREATE TABLE v ( i INTEGER,b BOOLEAN DEFAULT false
);

CREATE RULE _RETv ASON SELECT TO v DO INSTEADSELECT * FROM t;

CREATE RULE v_insert ASON INSERT TO v DO INSTEADINSERT INTO t values ( NEW.i, NEW.b);

Then when you do

INSERT INTO v VALUES(43);

the default defined for v.b gets applied by the parser, before the
rule substitution happens.

This still means you have two places that know the default, but
since they're both table declarations maybe it's not so bad.
        regards, tom lane